1. Field of the Invention (Technical Field)
The present invention relates to apparatuses and methods for electroplating and electrochemically modifying the surface finish of ferrous and magnetic powders, particularly by continuous magnetically assisted centrifugal means for encapsulation, and electrodeposition on powders without limitation on particle size, but specifically including submicron- or nano-sized particles.
2. Background Art
The technologies for electrochemical enhancement of the surfaces of the particles in bulk powders has previously been limited to two main types: chemical copper and electrolytic nickel auto-catalytic processes; and rotary electroplating devices which require frequent stopping and starting of the electrolytic cell's rotation to tumble the powder to achieve uniform dispersion of the coating upon the particles. A limitation of the previous art using chemical or auto-catalytic processes is the cost of the chemical consumption due to the enormous surface areas of powders. Another limitation of known devices using the rotary techniques is the need to stop the cell to tumble the powder in order to disperse the coating and prevent agglomeration of the particles. Known devices of the latter type known in the art are typified by the disclosure of U.S. Pat. No. 5,879,520, the teachings of which are hereby incorporated by reference. Further background in the field of rotary flow-through electroforming/electrodeposition devices and methods is supplied by U.S. Pat. Nos. 5,487,824 and 5,565,079, the disclosures of which are hereby incorporated by reference.
Previous rotary flow-through devices are capable of centrifugal clarification of the particles in solution and fixing them against the cathode ring for electrical contact. A disadvantage occurs, however, when rotation of the cell must be stopped to tumble the powder particles to foster even electrodeposition upon the individual particles. During this “stop phase,” the particles are re-suspended in the electrolyte solution. If the particles are of sufficient density, continuing the rotation of the cell re-clarifies the solution and again fixes the particles against the electrical contact ring, but the need periodically to stop and re-start cell rotation prolongs total processing times. But very significantly, in the case of submicron-sized, low mass powders, the method of repeatedly stopping and resuming cell rotation is unacceptable from a practical standpoint, because the material particles remain in suspension (rather than in contact with the cathode) for impermissibly, nearly indefinite, lengths of time.
Each time the cell rotation is resumed (after stopping to tumble the substrate powder), time is required to clarify the solution and re-fix the particles to the face of the cathode ring; heavier particles are thrown into renewed contact with the cathode first, while finer particles require comparatively more time to move outward under centrifugal force. This results in heavier particles having preferential electrical contact with the cathode, resulting in a wide variance in the uniformity of the thickness distribution. In many cases, ultrafine particles will receive no electrodeposition at all.